No more waste: special coating makes for packaging that can be emptied 100%

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Meat-eating pitcher plants served as a blueprint for this invention. Due to their extremely smooth surface inside prey cannot escape. Photo: Thomas Gronemeyer

No more waste: special coating makes for packaging that can be emptied 100%

There are not one but three drawbacks of food residues in packaging: they contribute to global food waste, increase the amount of packaging waste and often cause consumer frustration. The packaging industry has therefore already spent years researching ways to rise to this challenge. Now staff at the US university Virginia Tech seem to have made a commercially viable breakthrough.

TIGHTLY PACKED

What are SLIPS?

By Slippery Liquid-Infused Porous Surfaces, or SLIPS for short, we understand porous surfaces or absorbing polymers that keep chemically compatible oils at the surface thereby preventing them from adhering to the material. To this end the surfaces have to have a micro surface roughness that keeps the oil in its position through surface tension. SLIPS were first developed by researchers of the Wyss Institute at the America’s Harvard University in 2011.

Nature as blueprint

By their own accounts, the scientists were inspired by the meat-eating pitcher plant. Thanks to its smooth surface structure it is capable of catching insects while repelling any other undesirable materials at the same time. The SLIPS coating consists of silicon and fluorine-based absorbing polymers rather than nectar and digestion enzymes. These coatings have the ability to repel liquids and solids from almost any surface under virtually all conditions. Furthermore, they are self-cleaning and can also repair themselves in the event of damage. The technology is said to even work under high pressure, temperatures below zero and strong UV radiation. SLIPS can be generated on nearly all surfaces – including glass, plastics and metal. The coating as such is non-toxic and corrosion-resistant. However, there was one problem with the then novel technology: due to its high costs it was not attractive for industrial applications and therefore failed to become established on the market.

Proving particularly successful were small ketchup sachets from fast-food restaurants. Here, every bit of their contents is said to be removed by squeezing. Photo: Marco Verch / flickr.com, https://www.flickr.com/photos/149561324@N03/

Lower-cost further developments

The current study by researchers at Virginia Tech University in the USA is based on the same old basic principle. The scientists developed SLIPS with hydrocarbon-based polymers. The oils they used are compatible with plastics by nature, which is why the molecular structure of the material also features the required nano-roughness without any further external influence. The plastic surfaces coated with oil resist bacterial growth and adherence without requiring a separate roughening of the surface and, hence, additional time and expense. In future, it is planned to roll out this method for all everyday products; above and beyond food packaging it might also be of interest for the cosmetics and pharmaceutical sectors.

Recycling and health

Testing of recyclability has not been carried out yet. However, developers assume that the oil infusion will not interfere with the reusability of the plastics. Furthermore, they say the quantity of oil required for a smooth plastic film is extremely small at roughly one gram per square metre of packaging. And consumer health is not endangered since only high-quality vegetable oils are added to plastic surfaces rather than nano-particles of high risk for man.

Using the ‘LiquiGlide’ technology nearly complete emptying of ketchup bottles could be achieved. Photo: Varanasi Research Group

Same principle – different technology

2014 saw another technology hit the light of day - LiquiGlide – which again moved into the public eye in 2018. It changes the way liquids move in packaging. Here a slippery coating on plastic surfaces make especially viscous liquids slide easily. The liquid used for LiquiGlide works like a lubricant: it fills the gaps of rough, textured materials and thereby reduces the natural friction with the solid body.

Recycling and health

In the long run this coating can render the use of caps and pumps superfluous, which are currently required to remove contents. There is no nano-technology involved in these coatings. Health compatibility with the respective food was confirmed by the FDA (Food and Drug Administration).

One disadvantage of LiquiGlide is that it cannot cover all applications with one identical material. In fact each coating must be designed individually for the given use. Nearly complete emptying of packaging was achieved in tests with ketchup bottles. With bigger containers, however, the uniform application of the coating proves difficult. Furthermore, the special coatings are relatively expensive, which is why this innovative packaging solution is best suited for small containers for the time being.